On 14/06/2021 17:13, Andrew Cooper wrote: > +/* > + * Probe for how RTM behaves, deliberately not inspecting CPUID. > + * Distinguishes between "no support at all" (i.e. XBEGIN suffers #UD), > + * working ok, and appearing to always abort. > + */ > +static enum rtm_behaviour __attribute__((noclone)) probe_rtm_behaviour(void)
This doesn't compile, because Clang doesn't understand noclone. With it dropped, https://cirrus-ci.com/build/6399801072812032 is the FreeBSD build, confirming that sigill_handler() below is seemingly ok. ~Andrew > +{ > + for ( unsigned int i = 0; i < 1000; ++i ) > + { > + /* > + * Opencoding the RTM infrastructure from immintrin.h, because we > + * still support older versions of GCC. ALso so we can include #UD > + * detection logic. > + */ > +#define XBEGIN_STARTED -1 > +#define XBEGIN_UD -2 > + unsigned int status = XBEGIN_STARTED; > + > + asm volatile ( ".Lxbegin: .byte 0xc7,0xf8,0,0,0,0" /* XBEGIN 1f; 1: > */ > + : "+a" (status) :: "memory" ); > + if ( status == XBEGIN_STARTED ) > + { > + asm volatile ( ".byte 0x0f,0x01,0xd5" ::: "memory" ); /* XEND */ > + return RTM_OK; > + } > + else if ( status == XBEGIN_UD ) > + return RTM_UD; > + } > + > + return RTM_ABORT; > +} > + > +static struct sigaction old_sigill; > + > +static void sigill_handler(int signo, siginfo_t *info, void *extra) > +{ > + extern const char xbegin_label[] asm(".Lxbegin"); > + > + if ( info->si_addr == xbegin_label && > + memcmp(info->si_addr, "\xc7\xf8\x00\x00\x00\x00", 6) == 0 ) > + { > + ucontext_t *context = extra; > + > + /* > + * Found the XBEGIN instruction. Step over it, and update `status` > to > + * signal #UD. > + */ > +#if defined(__linux__) > +# ifdef __x86_64__ > + context->uc_mcontext.gregs[REG_RIP] += 6; > + context->uc_mcontext.gregs[REG_RAX] = XBEGIN_UD; > +# else > + context->uc_mcontext.gregs[REG_EIP] += 6; > + context->uc_mcontext.gregs[REG_EAX] = XBEGIN_UD; > +# endif > + > +#elif defined(__FreeBSD__) > +# ifdef __x86_64__ > + context->uc_mcontext.mc_rip += 6; > + context->uc_mcontext.mc_rax = XBEGIN_UD; > +# else > + context->uc_mcontext.mc_eip += 6; > + context->uc_mcontext.mc_eax = XBEGIN_UD; > +# endif > + > +#elif defined(__NetBSD__) > +# ifdef __x86_64__ > + context->uc_mcontext.__gregs[_REG_RIP] += 6; > + context->uc_mcontext.__gregs[_REG_RAX] = XBEGIN_UD; > +# else > + context->uc_mcontext.__gregs[_REG_EIP] += 6; > + context->uc_mcontext.__gregs[_REG_EAX] = XBEGIN_UD; > +# endif > + > +#else > +# error Unknown environment - please adjust > +#endif > + } > + else > + { > + /* > + * Not the SIGILL we're looking for... Restore the old handler and > + * try again. Will likely coredump as a result. > + */ > + sigaction(SIGILL, &old_sigill, NULL); > + } > +}
